Security barriers

ABSTRACT

A security barrier is disclosed for controlling the passage of vehicles along a vehicle throughway ( 16 ). The security barrier comprising upper and lower barrier members ( 20, 22, 120, 122, 220, 222, 320, 322 ). The upper barrier member ( 20, 120, 220, 320 ) is pivotally mounted for movement between a closed configuration, in which a barrier portion of said upper barrier member ( 20, 120, 220, 320 ) extends across the vehicle throughway ( 16 ), and an open configuration in which the barrier portion is raised to permit passage of a  10  vehicle along the vehicle throughway ( 16 ). The upper and lower barrier members ( 20, 22, 120, 122, 220, 222, 320, 322 ) are operably linked so that pivoting of the upper barrier member ( 20, 120, 220, 320 ) to the open configuration causes the lower barrier member ( 22, 122, 222, 322 ) to be lowered, and pivoting of the upper barrier member ( 20, 120, 220, 320 ) to the closed configuration causes the lower barrier member ( 22, 122, 222, 322 ) to be raised.

This invention relates to security barriers for controlling the access of vehicles along a vehicle throughway, and in particular to security barriers that include a pivoted barrier member.

There are many different forms of security barrier for controlling the access of vehicles along a vehicle throughway. One form of security barrier includes a drive assembly situated at one side of the vehicle throughway, and a barrier member pivotally mounted at one end to the drive assembly. In a closed configuration of the security barrier, the barrier member extends across the width of the vehicle throughway. In the closed configuration, the barrier member is orientated horizontally at a height above ground level that prevents the access of vehicles along the vehicle throughway. In order to allow vehicular access, the security barrier is moved into an open configuration by rotating the barrier member about its pivot until the barrier member is in a vertical orientation. Security barriers of this type are popular due to the relatively low cost of manufacture and installation, and high speed of operation.

A principal disadvantage associated with security barriers of this type is that, in order to provide a high level of security, the barrier member needs to have a high level of strength. Unfortunately, the stronger the barrier member, the more the barrier member generally weighs, and consequently the greater the power and time required to rotate the barrier member from a horizontal orientation to a vertical orientation. For this reason, conventional security barriers of this type do not generally provide a high level of security.

In order to attempt to overcome this disadvantage, security barriers have been developed that incorporate additional security features, such as bollards that rise out of the ground. However, such additional security features typically lower the speed of operation significantly. In addition, the cost of manufacturing and installing the security barrier is likely to be increased considerably.

There has now been devised an improved security barrier which overcomes or substantially mitigates the above-mentioned and/or other disadvantages associated with the prior art.

According to the invention, there is provided a security barrier for controlling passage of vehicles along a vehicle throughway, the security barrier comprising upper and lower barrier members, the upper barrier member being pivotally mounted for movement between a closed configuration, in which a barrier portion of said upper barrier member extends across the vehicle throughway, and an open configuration in which the barrier portion is raised to permit passage of a vehicle along the vehicle throughway, wherein the upper barrier member is operably linked to the lower barrier member such that pivoting of the upper barrier member to the open configuration causes the lower barrier member to be lowered and pivoting of the upper barrier member to the closed configuration causes the lower barrier member to be raised.

The security barrier according to the invention is advantageous principally because the provision of two barrier members increases the level of security provided by the security barrier without significantly increasing the cost of manufacture and installation. The lower barrier member of the invention is preferably used as a counterbalancing weight for the barrier portion of the upper barrier member, thereby reducing the power and time required to raise the barrier portion. The lower barrier member may therefore be formed in materials of greater weight and strength relative to the upper barrier member.

The upper barrier member is preferably pivotally mounted at a point between its ends. Hence, the upper barrier member preferably comprises the barrier portion that extends across the vehicle throughway, and an extension portion that extends to the other side of said pivot point. The extension portion of the upper barrier member is preferably operably linked to the lower barrier member such that the lower barrier member acts to counterbalance the weight of the barrier portion of the upper barrier member.

The lower barrier member, and the extension portion of the upper barrier member, are preferably operably linked by a mechanical linkage. The mechanical linkage preferably comprises a connecting member, which may be either rigid or flexible in form, that extends between the extension portion of the upper barrier member, and either the lower barrier member itself or an intermediate component that is itself mechanically linked to the lower barrier member.

Where the connecting member is rigid, the connecting member is preferably pivotally attached at one end to the extension portion of the upper barrier member, and attached to the lower barrier member at the other end. The rigid connecting member may also be pivotally attached to the lower barrier member.

In other embodiments, the length of the connecting member between the extension portion of the upper barrier member, and either the lower barrier member or the intermediate component, is variable. In particular, said length preferably increases as the lower barrier member is lowered and decreases as the lower barrier member is raised. In this case, the connecting member is preferably flexible, and the upper barrier member preferably includes a cam about which the flexible member travels such that the effective length of the connecting member varies as described above. The cam is preferably shaped so as to optimise the balance between the weight of the barrier portion, and the weight of the lower barrier member.

Most preferably, the lower barrier member is of greater weight and strength than the upper barrier member. The upper barrier member preferably pivots about a fixed point in a pillar or the like mounted to one side of the vehicle throughway. Such a pillar or the like preferably includes means for rotating the upper barrier member about the pivot axis. Such means may be manually operated, or may be driven by a motor. In the latter case, the means may be actuated by an operator or automatically under microprocessor control. For example, a microprocessor may cause the upper barrier member to be raised to the open configuration in response to a satisfactory security check. The security check may be performed in any conventional manner. For example, the security barrier may include a device for receiving security information, such as a keycard reader, microphone or keypad, and means for verifying the security information before activating the rotating means.

The free end of the barrier portion is preferably received, when the upper barrier member is in the closed configuration, within a support positioned adjacent the opposite side of the vehicle throughway to that at which the upper barrier member is pivotally mounted. Conveniently, such a support takes the form of a well in the upper surface of a pillar or the like that is mounted at that side of the vehicle throughway, or a ledge formed on such a pillar or between two pillars.

In a particularly preferred arrangement, the upper barrier member is pivotally mounted between two pillars at one side of the vehicle throughway, and the free end of the upper barrier member is received, in the closed configuration, between two pillars at the other side of the vehicle throughway.

The lower barrier member is preferably mounted by means of at least one pivoting linkage to a part of the security barrier that is stationary during use. The first pivoting linkage is preferably pivotally attached at one end to the lower barrier member, and at the other end to a part of the security barrier that is stationary during use. Said stationary part of the security barrier is preferably situated at the other side of the vehicle throughway to the extension portion of the upper barrier member. Where the lower barrier member is mounted by means of only one pivoting linkage, the pivoting linkage is preferably pivotally attached to a part of the security barrier that is situated above ground level.

For example, the lower barrier member may be connected by the pivoting linkage to a pillar or the like at that side of the vehicle throughway, which pillar may also be part of an assembly that receives and supports the free end of the upper barrier member when the latter is in the closed configuration. In this case, the lower barrier member is preferably suspended by pivoting linkages from the extension portion of the upper barrier member and the pillar at the other side of the vehicle throughway. In such an arrangement, in the closed configuration, the upper and lower barrier members and the two pivoting linkages by which the lower barrier member is suspended have a generally trapezoidal disposition, with the upper and lower barrier members preferably being disposed substantially parallel to each other and to the ground. By appropriate selection of the geometry of the linkages, an arrangement can be achieved in which the lower barrier member remains horizontal and parallel to the ground while it is lowered or raised by raising or lowering of the upper barrier member to the open or closed configuration.

In addition, the lower barrier member may be mounted by means of a second pivoting linkage to a further part of the security barrier that is stationary during use. The second pivoting linkage is preferably pivotally attached at one end to the lower barrier member, and at the other end to a part of the security barrier that is stationary during use. In particular, the second pivoting linkage is preferably pivotally attached to a part of the security barrier that is situated on the same side of the vehicle throughway as the extension portion of the upper barrier member. In this case, the first and second pivoting linkages preferably act on opposite ends of the lower barrier member.

The first and second pivoting linkages are preferably pivotally attached to a part of the security barrier that is at ground level. Most preferably, the first and second linkages are of identical length, and are orientated parallel to each other, such that the lower barrier member is maintained in a horizontal orientation at all times.

In the closed configuration, the upper barrier member extends across the vehicle throughway and represents a barrier to a vehicle travelling along the vehicle throughway. The lower barrier member is suspended beneath the upper barrier member and also extends across the vehicle throughway, above ground level.

When the upper barrier member is raised to the open configuration, the lower barrier member is lowered sufficiently to permit a vehicle to pass over it. The lower barrier member may be received within a channel formed in the ground surface such that the upper surface of the lower barrier member lies substantially flush with the ground level. The security barrier may include a ramp that is formed on the upper surface of the ground across the vehicle throughway, and includes a channel within which the lower barrier member may be received such that the upper surface of the lower barrier member lies substantially flush with the upper surface of the ramp. The ramp is preferably formed from suitable road-building materials, such as asphalt or concrete, and the side walls of the channel are preferably lined, and thereby supported, by one or more support members. These support members may also provide a suitable substrate for the pivoting attachment of any linkages.

Alternatively, the lower barrier member may have such a form that when it is lowered into abutment with the ground a vehicle is able to drive over it without undue hindrance. The lower barrier member may, for example, be formed with ramps at one or both sides. In such an arrangement, the lower barrier member may permit traffic flow only in one direction, or may permit traffic flow while at the same time having a speed-restricting (or traffic-calming) effect. Alternatively, the lower barrier member may change in form when it is lowered into engagement with the ground. For instance, elements of the lower barrier member that are disposed, in the closed configuration, perpendicular to the ground, may be hinged such that they rotate to parallel alignment with the ground.

The lower barrier member is preferably formed of a high strength material. The cross-sectional area of the lower barrier member is preferably greater than that of the upper barrier member so as to provide increased strength. The cross-sectional shape of the lower barrier member is preferably chosen so as to maximise the strength of the barrier in the event of impact by a vehicle. For example, the lower barrier member may be of channel section, and hence comprise a plate that is orientated in a horizontal plane and a pair of downwardly-depending side plates that are both orientated in vertical planes. In addition, the lower barrier member may include a high-strength cable along its length to provide additional strength in the event of an impact.

The lower barrier member preferably extends beyond one, or preferably, both of the pillars or the like at each side of the vehicle throughway. This will help to impede any attempt by a vehicle to gain access at either side of the security barrier. The lower barrier member is preferably adapted to deform when impacted by an oncoming vehicle so as to absorb the energy of impact and contain the vehicle on one side of the security barrier without breaking. In order to further strengthen the security barrier on impact by a vehicle, the ends of the lower barrier member are preferably enlarged.

The security barrier may include a pair of portal frames that together define the lateral limits of the vehicle throughway. Preferably, the portal frames each define an opening, and the lower barrier member is preferably arranged within these openings at all times during use. In this case, the portal frames provide an additional reinforcement in the event of a vehicle colliding with the lower barrier member.

The security barrier is preferably arranged so that a counterbalancing moment is exerted on the upper barrier member in the rotational direction opposite to that of the moment caused by the weight of the upper barrier member. Preferably, the counterbalance moment is predominantly caused by the weight of the lower barrier member.

Preferably, in order to minimise the energy required to raise and lower the upper barrier member between the closed and open configurations, the masses of the upper barrier member and the lower barrier member are selected so as to conserve gravitational potential energy between the closed and open positions. In approximate terms, this is achieved by equating the weight of the lower barrier member multiplied by the height through which its centre of gravity moves, to the weight of the upper barrier member multiplied by the height through which its centre of gravity moves.

In the majority of applications, the upper barrier member will have a length of less than 10 m, more typically less than 5 m, eg about 3-4 m. This will be sufficient for the majority of installations. However, where the vehicle throughway is particularly wide, it may be necessary to achieve an effective barrier width in excess of these figures, possibly as much as 20 m or more. In such cases, it may be appropriate for two (or more) upper barrier members to be operably linked to the lower barrier member. In a particularly preferred arrangement, the lower barrier member is suspended beneath two upper barrier members that are each pivotally mounted on a pillar or the like and are directed towards each other. The arrangement is thus essentially symmetrical and potentially offers a number of advantages, as follows:

a) the upper barrier members may be shorter in length than would be the case for a single upper barrier member spanning the same distance. This may lead to faster operation and/or fewer problems in high winds;

b) The presence of two motors, one associated with each upper barrier member may speed operation of the barrier, especially where the lower barrier member is particularly heavy;

c) Provided that the two upper barrier members are moved in synchronism, the lower barrier member will always remain horizontal when it is lowered.

The invention will now be described in greater detail, by way of illustration only, with reference to the accompanying drawings, in which

FIG. 1 is a plan view of a vehicle throughway and a first embodiment of a security barrier according to the invention in a closed configuration;

FIG. 2 is a cross-sectional view, along the line II-II in FIG. 1, of the security barrier in a closed configuration;

FIG. 3 is a cross-sectional view of the security barrier in a partially open configuration;

FIG. 4 is a cross-sectional view of the security barrier in a fully open configuration; and

FIG. 5 is a cross-sectional view of a second embodiment of a security barrier according to the invention in a closed configuration;

FIG. 6 is a cross-sectional view of a third embodiment of a security barrier according to the invention in a closed configuration;

FIG. 7 is a cross-sectional view of the third embodiment in a partially open configuration;

FIG. 8 is a cross-sectional view of a fourth embodiment of a security barrier according to the invention in a closed configuration; and

FIG. 9 is a cross-sectional view, which is orthogonal to the view of FIG. 8, of a lower barrier member and a ramp that both form part of the fourth embodiment.

FIGS. 1 and 2 show a security barrier according to the invention in a closed configuration. The security barrier comprises a drive assembly 12 and a slave assembly 14. The drive and slave assemblies 12, 14 are positioned on opposite sides of a vehicle throughway 16, and each comprise a pair of spaced-apart rectangular pillars. Vehicles move along the vehicle throughway 16 in the direction of the arrows in FIG. 1 (and/or the opposite direction).

The security barrier further comprises an upper barrier member 20 which is securely mounted, a short distance from one end of the member 20, about a drive axle 13 that extends between the upper ends of the pillars of the drive assembly 12. When the security barrier is in its closed configuration, the end of the upper barrier member 20 remote from the drive axle 13 rests upon a support platform 15 that extends between the upper ends of the pillars of the slave assembly 14.

The drive assembly 12 also includes means (not shown in the Figures) for imparting a rotational force on the drive axle 13. Such means could, for instance, comprise a hand-wheel that is rotated manually by an operator or, alternatively, an electric motor that is controlled either directly by an operator or automatically by a central processor. Where a motor rotates the drive axle 13, the motor is preferably enclosed within a pillar of the drive assembly 12. However, it will be clear to the skilled person that any means could be used that is capable of imparting sufficient rotational force upon the drive axle 13 to raise the upper barrier member 20 into a vertical orientation.

The security barrier further comprises a lower barrier member 22 which is of greater weight and strength than the upper barrier member 20. The lower barrier member 22 extends between the drive and slave assemblies 12, 14 directly below, and (in the closed configuration depicted in FIGS. 1 and 2) parallel to, the upper barrier member 20. The lower barrier member 22, however, is longer than the upper barrier member 20 and extends beyond both the drive and slave assemblies 12, 14.

The lower barrier member 22 is suspended from the upper barrier member and the slave assembly 14 respectively by first and second links 24,26. The first link 24 is pivotally connected at one end to the end of the upper barrier member 20 adjacent the drive axle 13. The other end of the first link 24 is connected to a part of the lower barrier member 22 that is situated within the drive assembly 12. In the embodiment illustrated, the lower end of the first link 24 is fixedly connected to the lower barrier member 22, at right angles thereto. The first link 24 is orientated vertically when the security barrier is in a closed configuration. In other embodiments, the lower end of the first link 24 may be pivotally connected to the lower barrier member 22, in which case the first link 24 will be inclined to the vertical when the security barrier is in the closed configuration. The pivotal connection is formed so that the upper barrier member 20 is rotatable relative to the lower barrier member 22 and the first link 24, within the limits imposed by the remainder of the security barrier, in a vertical plane which is orientated perpendicularly to the direction of motion of vehicles along the vehicle throughway 16.

The second link 26 is pivotally connected at one end to a pillar of the slave assembly 14 and at the other end to a part of the lower barrier member 22 that is positioned between the drive and slave assemblies 12, 14 in the closed configuration. The second link 26 is orientated at an angle to both the pillar of the slave assembly 14 and the lower barrier member 22. The pivotal connections are formed so that the second link 26 is rotatable relative to both the pillar of the slave assembly 14 and the lower barrier member 22, within the limits imposed by the remainder of the security barrier, in a vertical plane which is orientated perpendicularly to the direction of motion of vehicles along the vehicle throughway 16.

Referring also now to FIGS. 3 and 4, the security barrier is arranged so that if the drive axle 13 is rotated anti-clockwise (as viewed in FIGS. 2 to 4), and the upper barrier member 20 is therefore raised, the lower barrier member 22 is lowered, as shown in FIG. 3. As shown in FIGS. 3 and 4, the first link component 24 remains orientated vertically, the lower barrier member 22 remains orientated horizontally, and the second link component 26 rotates towards a vertical orientation, as the lower barrier member 22 is lowered. A trough 30 is formed across the vehicle throughway in a straight line between, and slightly beyond, the drive and slave assemblies 12, 14 so that when the upper barrier member 20 is raised fully, as shown in FIG. 4, the lower barrier member 22 is received within the trough 30, the upper surface of the lower barrier member 22 being substantially flush with the surface of the vehicle throughway.

In order to further strengthen the security barrier in the event of an impact by a vehicle, the lower barrier member 22 has enlarged end portions 23 that are of larger dimensions than the space between the pillars of the drive and slave assemblies 12, 14. The trough 30 includes enlarged end portions 32 so as to accommodate the enlarged portions 23 of the lower barrier member 22.

In the closed configuration of the security barrier, a counterbalance moment is exerted by the first link 24 upon the end of the upper barrier member 20 to which the first link 24 is pivotally connected. The counterbalance moment is caused by the resultant force exerted by the first link 24 upon the end of the upper barrier member 20. The analysis of the forces in the various links is amenable to simple static analysis for slow motion or to dynamic analysis in the case where motion is fast enough for inertia forces to be significant. The lengths, spatial orientation, speed of operation and masses of the links can be adjusted to achieve a wide variety of predictable resulting effects.

The security barrier is arranged so that, as the upper barrier member 20 is rotated from the closed configuration, in which the barrier moment is greater than the counterbalance moment, towards the open configuration, the counterbalance moment increases relative to the barrier moment. The security barrier will then reach an equilibrium configuration, situated between the closed and open configurations, in which the counterbalance moment is equal to the barrier moment. As the upper barrier member 20 is rotated further, from the equilibrium configuration towards the open configuration, the counterbalance moment increases further relative to the barrier moment and becomes greater than the barrier moment. In this way, a rotational force is required to rotate the upper barrier member 20 from the closed configuration to the equilibrium configuration but then the counterbalance moment will overcome the barrier moment to rotate the upper barrier member 20 from the equilibrium configuration to the open configuration. A counterbalance mass (not shown in the Figures) may be added to the end of the upper barrier member 20 adjacent the first link 24 so as to adjust the barrier and counterbalance moments, as required.

In order to minimise the energy required to raise and lower the upper barrier member 20 between the closed and open configurations, the masses of the upper barrier member 20 and the lower barrier member 22 are selected so as to conserve gravitational potential energy between the closed and open positions. In approximate terms, this is achieved by equating the weight of the lower barrier member 22 multiplied by the height through which its centre of gravity moves, to the weight of the upper barrier member 20 multiplied by the height through which its centre of gravity moves.

FIG. 5 shows a second embodiment of a security barrier according to the invention. The second embodiment differs from the first, illustrated in FIGS. 1 to 4, in that it comprises a single lower barrier member 122 that is suspended, not from a single upper barrier member and a slave assembly, but instead from a pair of upper barrier members 120. The upper barrier members 120 are broadly similar to the upper barrier member 20 of the first embodiment, each being pivotally mounted in a drive assembly 112 that houses a motor (not shown) by which the upper barrier member 120 can be rotated (about drive axles 113) from the closed configuration shown in FIG. 5 (in which the upper barrier member 120 is disposed substantially horizontally, in the path of a vehicle approaching the security barrier) to an open configuration (in which the upper barrier member 120 is raised to permit passage of the vehicle). As for the first embodiment, each drive assembly 112 comprises a pair of spaced-apart pillars, the upper barrier members 120 being mounted between the two pillars of the drive assembly 112.

The upper barrier members 120 are coupled to the lower barrier member 122 by pivoting links 124, each of which is connected at one end to a point near the end of the upper barrier member 120 adjacent the associated drive assembly 112 and at the other end to the lower barrier member 122. As can be seen from FIG. 5, the arrangement is symmetrical, with the two upper barrier members 120 meeting at the centre of the barrier. In other embodiments, the ends of the upper barrier members may overlap, eg by virtue of having cranked ends or by being slightly offset from one another.

In use, the upper barrier members 120 are raised to the open configuration by operation of the motors housed within the drive assemblies 112. This has the effect of lowering the lower barrier member 122. Provided that, as would normally be the case, the two motors are operated in synchronism, the symmetry of the barrier is maintained as the upper barrier members 120 are raised, and the lower barrier member 122 remains horizontal as it descends. As for the first embodiment, the lower barrier member 122 is received within a trough 130 formed in the ground beneath the barrier, enlarged end portions 123 of the lower barrier member 122 being received within correspondingly enlarged portions 132 of the trough 130.

FIGS. 6 and 7 show a third embodiment of a security barrier according to the invention. The third embodiment is identical to the first embodiment save for a pair of base links 226 which replace the second link 26, and a pair of support members that line the trough 230 along its side faces.

The base links 226 are of identical length, and are each pivotally connected at one end to a side face of the lower barrier member 222 and at the other end to one of the support members within the trough 230. The security barrier is arranged so that the base links 226 are always parallel relative to one another, and the lower barrier member 222 is maintained in a horizontal orientation.

When the security barrier is in its closed configuration, as shown in FIG. 6, the lower barrier member 222 is orientated horizontally in a raised position, and the base links 226 are inclined relative to both the lower barrier member 222 and the trough 230. As the upper barrier member 220 is rotated towards an open configuration, the lower barrier member 222 is lowered and the base links 226 rotate towards the trough 230, as shown in FIG. 7. When the security barrier has reached its fully open configuration, the lower barrier member 222 and the base links 226 will lie alongside one another within the trough 230.

The base link 226 arrangement of this embodiment ensures that the lower barrier member 222 does not deviate from a horizontal orientation during opening or closing of the security barrier.

FIGS. 8 and 9 show a fourth embodiment of a security barrier according to the invention. The fourth embodiment comprises drive and slave assemblies 312,314 that are similar to those of the first embodiment. The fourth embodiment also comprises a trough 330 of rectangular cross-section. This trough 330 is similar to the trough 230 of the first embodiment except that it is formed within a ramp 334 that traverses the vehicle throughway, as shown in FIG. 9. The ramp 334 is formed of a suitable road-building material, such as asphalt or concrete, and L-shaped support members 336 support the side walls of the trough 330.

An upper barrier member 320 extends in a horizontal orientation between the drive and slave assemblies 312,314 when the security barrier is in a closed configuration, as shown in FIG. 8. At one end, the upper barrier member is formed with a cam 316 on its upper surface that is securely attached to a drive axle 313. The rotating means of the drive assembly 312 acts to rotate the drive axle 313, and hence also the cam 316 and the upper barrier member 320, between a closed configuration of the security barrier in which the upper barrier member is orientated horizontally and a fully open configuration of the security barrier in which the upper barrier member is orientated vertically. In the closed configuration of the security barrier, the upper barrier member 320 rests upon a platform 315 extending between the two pillars of the slave assembly 314.

The fourth embodiment also has a lower barrier member 322 which has a cross-section that is rectangular and channel-shaped, and a pair of upstanding end portions. In particular, the lower barrier member 322 comprises an upper plate, which is orientated in a horizontal plane, and a pair of downwardly-depending side plates that are both orientated in vertical planes, as shown most clearly in FIG. 9. When the security barrier is in its open configuration, the lower barrier member 322 is accommodated within the trough 330. The lower barrier member 322 is formed so that, in this configuration, the upper plate forms a bridge across the trough 330 so that vehicles can drive smoothly over the ramp 334, the trough 330 and the lower barrier member 322.

In a similar manner to the third embodiment, base links 326 connect the lower barrier member 322 to one of the support members 336 within the trough 330. The base links 326 are of identical length, and are each pivotally connected at one end to a side face of the upstanding end portions of the lower barrier member 322 and at the other end to one of the support members 336 within the trough 330. The security barrier is arranged so that the base links 326 are always parallel relative to one another, and the lower barrier member 322 is maintained in a horizontal orientation.

A wire rope 317 is securely attached at one end to the side of the cam 316 that faces in the direction of the slave assembly 314. The wire rope 317 passes over the upper surface of the cam 316, and extends downwardly below the upper barrier member 320. An eye at the lower end of the wire rope 317 engages a trunnion bolted to the base link 326 that is adjacent to the drive assembly 312. The security barrier is arranged such that the wire rope 317 acts to raise the base link 326 that is adjacent to the drive assembly 312, and hence raise the lower barrier member 322, as the upper barrier member 320 is lowered from the open configuration of the security barrier to the closed configuration.

When the security barrier is in its closed configuration, as shown in FIG. 8, the lower barrier member 322 is orientated horizontally in a raised position, and the base links 326 are inclined relative to both the lower barrier member 322 and the trough 330. As the upper barrier member 320 is rotated towards an open configuration, the lower barrier member 322 is lowered and the base links 326 rotate towards the trough 330. When the security barrier has reached its fully open configuration, the lower barrier member 222 is fully accommodated within the trough 330, as described above with reference to FIG. 9.

The shape of the cam 316 is chosen so as to give the best possible balance at the drive axle 313 as the security barrier is being opened or closed. The cam 316 shown in FIG. 8 has a curved upper surface that has a gradually decreasing radius as the wire rope 317 extends towards the base link 326 to which the wire rope 317 is attached.

Finally, the fourth embodiment includes a pair of portal frames 340 that together define the lateral limits of the vehicle throughway. The portal frames 340 each define an opening, and the lower barrier member 322 is arranged within these openings at all times during use. The portal frames 340 therefore provide an additional reinforcement in the event of a vehicle colliding with the lower barrier member 322. Each portal frame 340 is formed from members that have a cross-section that is rectangular and channel-shaped for additional strength. In addition, the portal frames 340 need only be high enough to accommodate the lower barrier member 322 in its uppermost position. 

1. A security barrier for controlling passage of vehicles along a vehicle throughway, the security barrier comprising: upper and lower barrier members, the upper barrier member being pivotally mounted for movement between a closed configuration, in which a barrier portion of said upper barrier member extends across the vehicle throughway, and an open configuration in which the barrier portion is raised to permit passage of a vehicle along the vehicle throughway, the lower barrier member being mounted by at least one pivoting linkage to a part of the security barrier that is stationary during use, the at least one pivoting linkage being rotatable relative to the stationary part of the security barrier within a vertical plane that is orientated generally perpendicularly to the direction of motion of vehicles along the vehicle throughway, wherein the upper barrier member is operably linked to the lower barrier member such that pivoting of the upper barrier member to the open configuration causes the lower barrier member to be lowered and pivoting of the upper barrier member to the closed configuration causes the lower barrier member to be raised.
 2. A security barrier as claimed in claim 1, wherein the security barrier is arranged so that a counterbalancing moment is exerted on the upper barrier member in the rotational direction opposite to that of the moment caused by the weight of the upper barrier member.
 3. A security barrier as claimed in claim 2, wherein the counterbalance moment is predominantly caused by the weight of the lower barrier member.
 4. A security barrier as claimed in claim 3, wherein the upper barrier member is pivotally mounted at a point between its ends, the upper barrier member thereby comprising an extension portion that extends to the other side of said pivot point to the barrier portion, the extension portion of the upper barrier member being operably linked to the lower barrier member such that the lower barrier member acts to counterbalance the weight of the barrier portion of the upper barrier member.
 5. A security barrier as claimed in claim 4, wherein the lower barrier member and the extension portion of the upper barrier member are operably linked by a mechanical linkage.
 6. A security barrier as claimed in claim 5, wherein the mechanical linkage comprises a connecting member that extends between the extension portion of the upper barrier member, and the lower barrier member.
 7. A security barrier as claimed in claim 5, wherein the mechanical linkage comprises a connecting member that extends between the extension portion of the upper barrier member, and an intermediate component that is itself mechanically linked to the lower barrier member.
 8. A security barrier as claimed in claim 6, wherein the connecting member is rigid in form, and is pivotally attached to the extension portion of the upper barrier member.
 9. A security barrier as claimed in claim 6, wherein the length of the connecting member between the extension portion of the upper barrier member, and either the lower barrier member or the intermediate component, is variable such that said length increases as the lower barrier member is lowered and decreases as the lower barrier member is raised.
 10. A security barrier as claimed in claim 9, wherein the connecting member is flexible, and the upper barrier member includes a cam about which the flexible member travels such that the effective length of the connecting member is varied.
 11. A security barrier as claimed in claim 1, wherein the lower barrier member is connected by a first pivoting linkage to a pillar or the like at the other side of the vehicle throughway to the extension portion, the lower barrier member being suspended by pivoting linkages from the extension portion of the upper barrier member and the pillar at the other side of the vehicle throughway.
 12. A security barrier as claimed in claim 1, wherein the lower barrier member is mounted by first and second pivoting linkages, the first and second linkages being of identical length and orientated parallel to each other such that the lower barrier member is maintained in a horizontal orientation at all times.
 13. A security barrier as claimed in claim 1, wherein the lower barrier member is received within a channel formed in the ground surface such that the upper surface of the lower barrier member lies substantially flush with the ground level.
 14. A security barrier as claimed in claim 1, wherein the security barrier includes a ramp that is formed on the upper surface of the ground across the vehicle throughway, and includes a channel within which the lower barrier member is received such that the upper surface of the lower barrier member lies substantially flush with the upper surface of the ramp.
 15. A security barrier as claimed in claim 14, wherein the ramp is formed from suitable road-building materials, and the side walls of the channel are lined, and thereby supported, by one or more support members.
 16. A security barrier as claimed in claim 1, wherein the lower barrier member has such a form that when it is lowered into abutment with the ground a vehicle is able to drive over it without undue hindrance.
 17. A security barrier as claimed in claim 1, wherein the lower barrier member is of greater weight and strength than the upper barrier member.
 18. A security barrier as claimed in claim 17, wherein the cross-sectional shape of the lower barrier member is chosen so as to maximise the strength of the security barrier in the event of impact by a vehicle.
 19. A security barrier as claimed in claim 18, wherein the lower barrier member is of channel section.
 20. A security barrier as claimed in claim 1, wherein the upper barrier member pivots about a fixed point in a pillar or the like mounted to one side of the vehicle throughway, said pillar or the like including means for rotating the upper barrier member about a pivot axis.
 21. A security barrier as claimed in claim 20, wherein the free end of the barrier portion is received, when the upper barrier member is in the closed configuration, within a support positioned adjacent the opposite side of the vehicle throughway to that at which the upper barrier member is pivotally mounted.
 22. A security barrier as claimed in claim 21, wherein the upper barrier member is pivotally mounted between two pillars at one side of the vehicle throughway, and the free end of the upper barrier member is received, in the closed configuration, between two pillars at the other side of the vehicle throughway.
 23. A security barrier as claimed in claim 22, wherein the lower barrier member extends beyond both of the pillars at each side of the vehicle throughway.
 24. A security barrier as claimed in claim 23, wherein the ends of the lower barrier member are enlarged.
 25. A security barrier as claimed in claim 1, wherein the security barrier includes a pair of portal frames that together define the lateral limits of the vehicle throughway.
 26. A security barrier as claimed in claim 25, wherein the portal frames each define an opening, and the lower barrier member is arranged within these openings at all times during use.
 27. A security barrier as claimed in claim 1, wherein the masses of the upper barrier member and the lower barrier member are selected so as to conserve gravitational potential energy between the closed and open configurations.
 28. A security barrier as claimed in claim 1, wherein the lower barrier member is suspended beneath two upper barrier members that are each pivotally mounted on a pillar or the like and are directed towards each other.
 29. A method for making a security barrier for controlling passage of vehicles along a vehicle throughway, the method comprising: pivotally mounting at least one upper barrier member for movement between a closed configuration and an open configuration; and mounting at least one lower barrier member with at least one pivoting linkage to a part of the security barrier that is stationary during use, the at least one pivoting linkage being rotatable relative to a base; wherein the upper barrier member is operably linked to the lower barrier member such that pivoting of the upper barrier member to the open configuration causes the lower barrier member to be lowered and pivoting of the upper barrier member to the closed configuration causes the lower barrier member to be raised.
 30. A security barrier for controlling passage of vehicles along a vehicle throughway, the security barrier comprising: two or more upper barrier members; at least one lower barrier member; the two or more upper barrier members are each pivotally mounted for movement between a closed configuration, in which a barrier portion of each of the two or more upper barrier members extends across at least a portion of the vehicle throughway, and an open configuration in which the barrier portion of each of the two or more upper barrier members is raised to permit passage of a vehicle along the vehicle throughway, the lower barrier member is mounted by at least one pivoting linkage to a part of the security barrier that is stationary during use, the at least one pivoting linkage is rotatable relative to the stationary part of the security barrier within a vertical plane that is orientated generally perpendicularly to the direction of motion of vehicles along the vehicle throughway, wherein the two or more upper barrier members are operably linked to the lower barrier member such that pivoting of the two or more upper barrier members to the open configuration causes the lower barrier member to be lowered and pivoting of the two or more upper barrier members to the closed configuration causes the lower barrier member to be raised. 